For the purposes of productivity improvement and adjustability of body color in a coating process line for vehicle bodies, various processes are performed, such as processes for an electrodeposition coat (under coat), intermediate coat and topcoat and antirust treatment, in a state in which lid parts such as doors and hoods are attached to main shell bodies. In the processes for an intermediate coat and topcoat, the vehicle body as an object to be coated is placed on a transfer trolley, applied with paint while being conveyed in a paint coating booth, and followed by a baking process in which the vehicle body, together with the transfer trolley, is carried into a paint baking oven to perform baking of a wet coating film. The paint baking oven used in the coating process line is configured such that a tunnel-shaped oven body is provided with an air supply duct for hot air and the hot air is blown to the whole vehicle body, which is being conveyed in the oven body, to bake the wet coating film (See Japanese Patent Application Publication No. JP06-000225).
A baking curable-type paint is used for vehicle bodies. The quality assurance standard for the cured coating film is, for example, holding of 140° C.×20 minutes for an intermediate paint and topcoat paint. In the conventional paint baking oven, however, the hot air is less likely to go around into narrow portions, such as those around hinges of doors, because of the structure of the vehicle body as compared with the body exterior parts to which the hot air is easy to blow. Thus, unfortunately, the narrow portions cannot readily satisfy the above-described quality assurance standard, such as holding of 140° C.×20 minutes.